E5531, a pure endotoxin antagonist of high potency

Hydrocarbon rulers in UDP-N-acetylglucosamine acyltransferases

UDP-GlcNAc acyltransferase (LpxA), the first enzyme of lipid A biosynthesis, catalyzes the transfer of an acyl chain activated on acyl carrier protein (ACP) to UDP-GlcNAc. LpxAs are very selective for the lengths of their acyl donor substrates. Escherichia coli LpxA prefers R-3-hydroxymyristoyl-ACP to R-3-hydroxydecanoyl-ACP by a factor of approximately 1000, whereas Pseudomonas aeruginosa LpxA prefers the opposite. E. coli G173M LpxA and the reciprocal P. aeruginosa M169G LpxA show reversed substrate selectivity in vitro and in vivo, demonstrating the existence of precise hydrocarbon rulers in LpxAs.

CD11/CD18 and CD14 Share a Common Lipid A Signaling Pathway

The activation of phagocytes by the lipid A moiety of LPS has been implicated in the pathogenesis of Gram-negative sepsis. While two LPS receptors, CD14 and CD11/CD18, have been associated with cell signaling, details of the LPS signal transduction cascade remain obscure. CD14, which exists as a GPI-anchored and a soluble protein, lacks cytoplasmic-signaling domains, suggesting that an ancillary molecule is required to activate cells. The CD11/CD18 integrins are transmembrane proteins. Like CD14, they are capable of mediating LPS-induced cellular activation when expressed on the surface of hamster fibroblasts Chinese hamster ovary (CHO)-K1. The observation that a cytoplasmic deletion mutant is still capable of activating transfected CHO-K1 argues that CD11/CD18 also utilizes an associated signal transducer. We sought to identify further similarities between the signaling systems utilized by CD14 and CD11/CD18. LPS-binding protein, which transfers LPS to CD14, enhanced both LPS-induced cellular activation and binding of Gram-negative bacteria in CD11/CD18-transfected CHO-K1, thus implying that LPS-binding protein can also transfer LPS to CD11/CD18. When synthetic lipid A analogues were analyzed for their ability to function as LPS agonists, or antagonists, in the CHO transfectants, we found the effects were identical regardless of which LPS receptor was expressed. This supports the hypothesis that a receptor distinct from CD14 and CD11/CD18 is responsible for discriminating between the lipid A of LPS and the LPS antagonists. We propose that this receptor, which is the target of the LPS antagonists, functions as the true signal transducer in LPS-induced cellular activation for both CD14 and CD11/CD18.

Tumor necrosis factor- alpha production to lipopolysaccharide stimulation by donor cells predicts the severity of experimental acute graft-versus-host disease

Donor T cell responses to host alloantigen are known predictors for graft-versus-host disease (GVHD); however, the effect of donor responsiveness to an inflammatory stimulus such as lipopolysaccharide (LPS) on GVHD severity has not been investigated. To examine this, we used mouse strains that differ in their sensitivity to LPS as donors in an experimental bone marrow transplant (BMT) system. Lethally irradiated (C3FeB6)F1 hosts received BMT from either LPS-sensitive (LPS-s) C3Heb/Fej, or LPS-resistant (LPS-r) C3H/ Hej donors. Mice receiving LPS-r BMT developed significantly less GVHD as measured by mortality and clinical score compared with recipients of LPS-s BMT, a finding that was associated with significant decreases in intestinal histopathology and serum LPS and TNF-alpha levels. When donor T cell responses to host antigens were measured, no differences in proliferation, serum IFN-gamma levels, splenic T cell expansion, or CTL activity were observed after LPS-r or LPS-s BMT. Systemic neutralization of TNF-alpha from day -2 to +6 resulted in decreased intestinal pathology, and serum LPS levels and increased survival after BMT compared with control mice receiving Ig. We conclude that donor resistance to endotoxin reduces the development of acute GVHD by attenuating early intestinal damage mediated by TNFalpha. These data suggest that the responsiveness of donor accessory cells to LPS may be an important risk factor for acute GVHD severity independent of T cell responses to host antigens.

Suppression of murine endotoxin response by E5531, a novel synthetic lipid A antagonist

As a consequence of blood-borne bacterial sepsis, endotoxin or lipopolysaccharide (LPS) from the cell walls of gram-negative bacteria can trigger an acute inflammatory response, leading to a series of pathological events and often resulting in death. To block this inflammatory response to endotoxin, a novel lipid A analogue, E5531, was designed and synthesized as an LPS antagonist, and its biological properties were examined in vitro and in vivo. In murine peritoneal macrophages, E5531 inhibited the release of tumor necrosis factor alpha (TNF-alpha) by Escherichia coli LPS with a 50% inhibitory concentration (IC50) of 2.2 nM, while E5531 elicited no significant increases in TNF-alpha on its own. In support of a mechanism consistent with antagonism of binding to a cell surface receptor for LPS, E5531 inhibited equilibrium binding of radioiodinated LPS ([125I]2-(r-azidosalicylamido)-1, 3'-dithiopropionate-LPS) to mouse macrophages with an IC50 of 0.50 microM. E5531 inhibited LPS-induced increases in TNF-alpha in vivo when it was coinjected with LPS into C57BL/6 mice primed with Mycobacterium bovis bacillus Calmette-Guérin (BCG). In this model, the efficacy of E5531 was inversely correlated to the LPS challenge dose, consistent with a competitive antagonist-like mechanism of action. Blockade of the inflammatory response by E5531 could further be demonstrated in other in vivo models: E5531 protected BCG-primed mice from LPS-induced lethality in a dose-dependent manner and suppressed LPS-induced hepatic injury in Propionibacterium acnes-primed or galactosamine-sensitized mice. These results argue that the novel synthetic lipid A analogue E5531 can antagonize the action of LPS in in vitro and suppress the pathological effects of LPS in vivo in mice.

The effect of the lipid A analog E5531 on phospholipid membrane properties

In order to determine the effect of the lipid A analog, E5531, on phospholipid membranes, we used dipalmitoylphosphatidylcholine (DPPC) and investigated the physicochemical interaction between E5531 and DPPC membranes. E5531 and DPPC are miscible in the bulk phase at 25 degrees C. Within the E5531 mole fraction range (X(E5531)) of 0-0.5, E5531 decreased the zeta potentials of DPPC membranes but did not change the size of the DPPC liposomes. E5531/DPPC mixtures formed liposome-like structures. E5531 increased the fluidity of the DPPC membrane and decreased pyrene diffusion in the membrane. E5531 decreased the phase transition temperature and the cooperative interactions between DPPC molecules. These effects of E5531 on phospholipid membranes were different from those of lipid A from Escherichia coli and Salmonella minnesota.

Innate immune recognition of bacterial lipopolysaccharide: dependence on interactions with membrane lipids and endocytic movement

Lipopolysaccharide ([LPS], an endotoxin) from most bacterial species provokes a strong inflammatory response in naive animals. LPS from Rhodobacter sphaeroides (RsLPS) has a relatively small hydrophobic region and does not stimulate cells or animals but instead acts as antagonist of LPS action. Here, we show that the activity of RsLPS is transformed from antagonist to full agonist by the addition of chlorpromazine (CPZ) and other cationic membrane-active agents. In addition, while LPS is rapidly transported from the plasma membrane to an intracellular site, we find that RsLPS is not transported but instead remains in the cell periphery. Addition of CPZ also reverses this behavior, causing RsLPS to be transported to a perinuclear site. The data suggest that the interaction of LPS with membrane lipids is influenced by membrane-modifying agents such as CPZ, and these interactions dictate both its intracellular transport and its ability to stimulate cellular responses.

Protective effects of a human 18-kilodalton cationic antimicrobial protein (CAP18)-derived peptide against murine endotoxemia

CAP18 (an 18-kDa cationic antimicrobial protein) is a granulocyte-derived protein that can bind lipopolysaccharide (LPS) and inhibit various activities of LPS in vitro. The present study examined the protective effect of a synthetic 27-amino-acid peptide (CAP18(109-135)) from the LPS-binding domain of CAP18 against antibiotic-induced endotoxin shock, using highly LPS-sensitive D-(+)-galactosamine (D-GalN)-sensitized C3H/HeN mice. The antibiotic-induced endotoxin (CAZ-endotoxin) was prepared from the culture filtrate of Pseudomonas aeruginosa PAO1 exposed to ceftazidime (CAZ). Injection of CAP18(109-135) protected the mice injected with LPS or CAZ-endotoxin from death and lowered their tumor necrosis factor (TNF) levels in serum in a dose-dependent manner. Treatment with CAZ caused death of the D-GalN-sensitized P. aeruginosa PAO-infected mice within 48 h, while injection with CAP18(109-135) rescued the mice from death. In the mice rescued from death by injection with CAP18(109-135), endotoxin levels in plasma and TNF production by liver tissues were decreased but the numbers of viable infecting bacteria in their blood were not decreased significantly and remained at the levels in CAZ-treated mice. These results indicate that CAP18(109-135) is capable of preventing antibiotic-induced endotoxic shock in mice with septicemia and that the effect is due to its LPS-neutralizing activity rather than to its antibacterial activity.

Antibacterial and anti-inflammatory agents that target endotoxin

Antibiotic-resistant bacterial infections are a major clinical problem. Lipid A, the active part of lipopolysaccharide endotoxins in Gram-negative bacteria, is an intriguing target for new antibacterial and anti-inflammatory agents. Inhibition of lipid A biosynthesis kills most Gram-negative bacteria, increases bacterial permeability to antibiotics and decreases endotoxin production.

Antibiotic treatment of experimental pneumonic plague in mice

A mouse model was developed to evaluate the efficacy of antibiotic treatment of pneumonic plague; streptomycin was compared to antibiotics with which there is little or no clinical experience. Infection was induced by inhalation of aerosolized Yersinia pestis organisms. Antibiotics were administered by intraperitoneal injection every 6 hours for 5 days, at doses that produced levels of drug in serum comparable to those observed in humans treated for other serious infections. These studies compared in vitro to in vivo activity and evaluated the efficacy of antibiotics started at different times after exposure. Early treatment (started 24 h after challenge, when 0 of 10 mice tested had positive blood cultures) with netilmicin, ciprofloxacin, ofloxacin, ceftriaxone, ceftazidime, aztreonam, ampicillin, and rifampin (but not cefazolin, cefotetan, or ceftizoxime) demonstrated efficacy comparable to streptomycin. Late treatment (started 42 h after exposure, when five of five mice tested had positive blood cultures) with netilmicin, ciprofloxacin, ofloxacin, and a high dose (20 mg/kg of body weight every 6 h) of gentamicin produced survival rates comparable to that with streptomycin, while all of the beta-lactam antibiotics (cefazolin, cefotetan, ceftriaxone, ceftazidime, aztreonam, and ampicillin) and rifampin were significantly inferior to streptomycin. In fact, all groups of mice treated late with beta-lactam antibiotics experienced accelerated mortality rates compared to normal-saline-treated control mice. These studies indicate that netilmicin, gentamicin, ciprofloxacin, and ofloxacin may be alternatives for the treatment of pneumonic plague in humans. However, the beta-lactam antibiotics are not recommended, based upon poor efficacy in this mouse model of pneumonic plague, particularly when pneumonic plague may be associated with bacteremia.

The significance of endotoxin release in experimental and clinical sepsis in surgical patients--evidence for antibiotic-induced endotoxin release?

Sepsis and peritonitis remain a serious challenge for surgical patients, despite improvement in surgical therapy and intensive care and the introduction of new powerful antibiotics. Recent in vitro studies revealed the potential of certain antibiotics, e.g. penicillin-binding protein (PBP) 3-specific antibiotics, to cause antibiotic-induced endotoxin release. Other types of antibiotics, e.g., PBP 2-specific antibiotics, were associated with no or less endotoxin release. Further in vitro experiments and investigations in animals support the hypothesis of antibiotic-induced endotoxin release, but there is little clinical evidence. The clinical significance of endotoxin is subject of open dispute with many pro's and contra's. Endotoxin, although an important trigger, may not be the only factor to induce cytokine release, e.g., peptidoglycans were able to stimulate cells to release cytokines. Gram-positive pathogens have gained more importance in clinical sepsis and may not be sufficiently reflected in current clinical studies. The hypothesis that neutralization of endotoxin and pro-inflammatory cytokines is beneficial in sepsis was seriously challenged by the results of recent clinical and experimental studies. The better understanding of mechanisms in endotoxin-induced cell activation and cell, cell-receptor and soluble receptor interactions led to new treatment options. Recent reports on the complex pathogenesis of peritonitis and the detection of pathogen-related factors with intraperitoneal immune response may have implications on clinical studies investigating the potential of new compounds and the effect of antibiotics on endotoxin release. However, only few reports are available on the clinical significance of antibiotic-induced endotoxin release, and association of endotoxin release with pathogens, mortality or alteration of physiological parameters were not observed. With regard to the particulars of these studies, e.g., a small study population or low mortality rate, mortality may not be an ideal outcome parameter for these studies. There is clinical evidence for antibiotic-induced endotoxin release. However, the need for well-designed and performed studies using newly developed monitoring devices in intensive care therapy is obvious.

A nonsubstituted primary hydroxyl group in position 6' of free lipid A is required for binding of lipid A monoclonal antibodies

Lipid A monoclonal antibodies, which require for binding the presence of the bisphosphorylated D-glucosamine disaccharide lipid A backbone, were tested against synthetic lipid A precursor Ia and compound B 1047 by enzyme immunoassay. The last-named compound is a precursor Ia analog with a methoxy instead of a hydroxy group at C6' and was chosen to determine why these antibodies failed to recognize the bound lipid A present in lipopolysaccharide (LPS). Whereas all antibodies tested bound to precursor Ia, none of them bound to compound B 1047 or Escherichia coli Re LPS to a significant extent. Compared to the natural substituent at C6', i.e., 3-deoxy-D-manno-octulosonic acid (Kdo), the methoxy group is neither bulky nor charged. Thus, the data suggest that it is not hindrance by Kdo but rather the generation of a neoantigen that endows lipid A with immunoreactivity upon liberation from LPS by acid hydrolysis.

Identification of the gene encoding the Escherichia coli lipid A 4'-kinase. Facile phosphorylation of endotoxin analogs with recombinant LpxK

The genes for seven of nine enzymes needed for the biosynthesis of Kdo2-lipid A (Re endotoxin) in Escherichia coli have been reported. We have now identified a novel gene encoding the lipid A 4'-kinase (the sixth step of the pathway). The 4'-kinase transfers the gamma-phosphate of ATP to the 4'-position of a tetraacyldisaccharide 1-phosphate intermediate (termed DS-1-P) to form tetraacyldisaccharide 1,4'-bis-phosphate (lipid IVA). The 4'-phosphate is required for the action of distal enzymes, such as Kdo transferase and also renders lipid A substructures active as endotoxin antagonists or mimetics. Lysates of E. coli generated using individual lambda clones from the ordered Kohara library were assayed for overproduction of 4'-kinase. Only one clone, [218]E1D1, which directed 2-2.5-fold overproduction, was identified. This construct contains 20 kilobase pairs of E. coli DNA from the vicinity of minute 21. Two genes related to the lipid A system map in this region: msbA, encoding a putative translocator, and kdsB, the structural gene for CMP-Kdo synthase. msbA forms an operon with a downstream, essential open reading frame of unknown function, designated orfE. orfE was cloned into a T7 expression system. Washed membranes from cells overexpressing orfE display approximately 2000-fold higher specific activity of 4'-kinase than membranes from cells with vector alone. Membranes containing recombinant, overexpressed 4'-kinase (but not membranes with wild-type kinase levels) efficiently phosphorylate three DS-1-P analogs: 3-aza-DS-1-P, base-treated DS-1-P, and base-treated 3-aza-DS-1-P. A synthetic hexaacylated DS-1-P analog, compound 505, can also be phosphorylated by membranes from the overproducer, yielding [4'-32P] lipid A (endotoxin). The overexpressed lipid A 4'-kinase is very useful for making new 4'-phosphorylated lipid A analogs with potential utility as endotoxin mimetics or antagonists. We suggest that orfE is the structural gene for the 4'-kinase and that it be redesignated lpxK.

Shortened hydroxyacyl chains on lipid A of Escherichia coli cells expressing a foreign UDP-N-acetylglucosamine O-acyltransferase

The first reaction of lipid A biosynthesis in Gram-negative bacteria is catalyzed by UDP-N-acetylglucosamine (UDP-GlcNAc) O-acyltransferase, the product of the lpxA gene. The reaction involves the transfer of an acyl chain from hydroxyacyl-acyl carrier protein (ACP) to the glucosamine 3-OH position of UDP-GlcNAc. The lipid A isolated from Escherichia coli contains (R)-3-hydroxymyristate at the 3 and 3' positions. Accordingly, LpxA of E. coli is highly selective for (R)-3-hydroxymyristoyl-ACP over ACP thioesters of longer or shorter acyl chains. We now demonstrate that the lpxA gene from Neisseria meningitidis encodes a similar acyltransferase that selectively utilizes 3-hydroxylauroyl-ACP. Strains of E. coli harboring the temperature-sensitive lpxA2 mutation make very little lipid A and lose viability rapidly at 42 degrees C. We have created an E. coli strain in which the chromosomal lpxA2 mutation is complemented by the N. meningitidis lpxA gene introduced on a plasmid. This strain, RO138/pTO6, grows similarly to wild type cells at 42 degrees C and produces wild type levels of lipid A. However, the lipid A isolated from RO138/pTO6 contains mostly hydroxylaurate and hydroxydecanoate in the 3 and 3' positions. The strain RO138/pTO6 is more susceptible than wild type to certain antibiotics at 42 degrees C. This is the first report of an E. coli strain growing with shortened hydroxyacyl chains on its lipid A. The lpxA gene product appears to be a critical determinant of the length of the ester-linked hydroxyacyl chains found on lipid A in living cells.

Pathobiology of lipopolysaccharide

Lipopolysaccharide is a component of the gram-negative bacterial cell wall that is responsible for 25,000-50,000 deaths in the United States each year. The sequelae of gram-negative infection and septicemia leading to death include fever, hypotension with inadequate tissue perfusion, and disseminated intravascular coagulation. It is clear that different cell types respond differently to lipopolysaccharide. Furthermore, various autacoids and cytokines are released that can affect cellular function even in cell types that do not recognize lipopolysaccharide. Despite advances made in the etiology of septic shock and organ failure, therapy is still for the most part supportive and largely ineffective. The aim of this review is to summarize the current understanding of the role of lipopolysaccharide in the development of septicemia by examining signal transduction and therapeutic approaches.

Confirmation of the structure of lipid A derived from the lipopolysaccharide of Rhodobacter sphaeroides by a combination of MALDI, LSIMS, and tandem mass spectrometry

The chemical structure of nontoxic diphosphoryl lipid A from Rhodobacter sphaeroides was confirmed using a combination of LSIMS (on a two-sector mass spectrometer) and MALDI (on time-of-flight and ion trap mass spectrometers) in conjunction with tandem mass spectrometry in both positive and negative ion modes. Accurate molecular weight measurement accompanied by the analysis of fragment ion masses yielded the composition of fatty acyl groups. Tandem experiments (collisionally induced dissociation of both quasimolecular and oxonium ions) were also performed, revealing the precise location and nature of the fatty acyl groups on the disaccharide backbone.

Inhibition of lipopolysaccharide-induced transcription factor Sp1 binding by spectrally pure diphosphoryl lipid A from Rhodobacter sphaeroides, protein kinase inhibitor H-8, and dexamethasone

The transcription factor Sp1 plays a crucial role in the monocyte-specific expression of CD14, a binding site (or putative receptor) for lipopolysaccharide (LPS) complexes with LPS-binding protein (LBP). By using RAW 264.7 macrophages treated with spectrally pure deep-rough-chemotype hexa-acyl LPS from Escherichia coli D31m4, three inhibitors were found to block the binding activity of transcription factor Sp1, as measured by electrophoretic mobility shift assays. These inhibitors were diphosphoryl lipid A from Rhodobacter sphaeroides (10 microg/ml); the isoquinoline-sulfonamide H-8 (10 and 100 microM), which is thought to be a cGMP-dependent protein kinase inhibitor; and the anti-inflammatory agent dexamethasone (10 microM).

A special acyl carrier protein for transferring long hydroxylated fatty acids to lipid A in Rhizobium

Lipid A, the hydrophobic anchor of lipopolysaccharides in the outer membranes of Gram-negative bacteria, varies in structure among different Rhizobiaceae. The Rhizobium meliloti lipid A backbone, like that of Escherichia coli, is a beta1'-6-linked glucosamine disaccharide that is phosphorylated at positions 1 and 4'. Rhizobium leguminosarum lipid A lacks both phosphates, but contains aminogluconate in place of the proximal glucosamine 1-phosphate, and galacturonic acid instead of the 4'-phosphate. A peculiar feature of the lipid As of all Rhizobiaceae is acylation with 27-hydroxyoctacosanoic acid, a long hydroxylated fatty acid not found in E. coli. We now describe an in vitro system, consisting of a membrane enzyme and a cytosolic acyl donor from R. leguminosarum, that transfers 27-hydroxyoctacosanoic acid to (Kdo)2-lipid IVA, a key lipid A precursor common to both E. coli and R. leguminosarum. The 27-hydroxyoctacosanoic acid moiety was detected in the lipid product by mass spectrometry. The membrane enzyme required the presence of Kdo residues in the acceptor substrate for activity. The cytosolic acyl donor was purified from wild-type R. leguminosarum using the acylation of (Kdo)2-[4'-32P]-lipid IVA as the assay. Amino-terminal sequencing of the purified acyl donor revealed an exact 19-amino acid match with a partially sequenced gene (orf*) of R. leguminosarum. Orf* contains the consensus sequence, DSLD, for attachment of 4'-phosphopantetheine. When the entire orf* gene was sequenced, it was found to encode a protein of 92 amino acids. Orf* is a new kind of acyl carrier protein because it is only approximately 25% identical both to the constitutive acyl carrier protein (AcpP) and to the inducible acyl carrier protein (NodF) of R. leguminosarum. Mass spectrometry of purified active Orf* confirmed the presence of 4'-phosphopantetheine and 27-hydroxyoctacosanoic acid in the major species. Smaller mass peaks indicative of Orf* acylation with hydroxylated 20, 22, 24, and 26 carbon fatty acids were also observed. Given the specialized function of Orf* in lipid A acylation, we suggest the new designation AcpXL.

Antiendotoxin activity of cationic peptide antimicrobial agents

The endotoxin from gram-negative bacteria consists of a molecule lipopolysaccharide (LPS) which can be shed by bacteria during antimicrobial therapy. A resulting syndrome, endotoxic shock, is a leading cause of death in the developed world. Thus, there is great interest in the development of antimicrobial agents which can reverse rather than promote sepsis, especially given the recent disappointing clinical performance of antiendotoxin therapies. We describe here two small cationic peptides, MBI-27 and MBI-28, which have both antiendotoxic and antibacterial activities in vitro and in vivo in animal models. We had previously demonstrated that these peptides bind to LPS with an affinity equivalent to that of polymyxin B. Consistent with this, the peptides blocked the ability of LPS and intact cells to induce the endotoxic shock mediator, tumor necrosis factor (TNF), upon incubation with the RAW 264.7 murine macrophage cell line. MBI-28 was equivalent to polymyxin B in its ability to block LPS induction of TNF by this cell line, even when added 60 min after the TNF stimulus. Furthermore, MBI-28 offered significant protection in a galactosamine-sensitized mouse model of lethal endotoxic shock. This protection correlated with the ability of MBI-28 to reduce LPS-induced circulating TNF by nearly 90% in this mouse model. Both MBI-27 and MBI-28 demonstrated antibacterial activity against gram-negative bacteria in vitro and in vivo against Pseudomonas aeruginosa infections in neutropenic mice.

A lipid A analog inhibits LPS-induced cytokine expression and improves survival in endotoxemic mice

It has recently been shown that inactive disaccharidic analogs of lipid A, an essential structure of lipopolysaccharide (LPS), may act as LPS antagonists which would be effective against septic shock induced by gram-negative bacteria endotoxin. In the present study we examined the inhibitory effect of DY-9973, a synthetic monosaccharidic lipid A analog, on LPS-induced cytokine expression in macrophages and lethal toxicity in mice. DY-9973 inhibited TNF-alpha production induced by LPS in human monocytes and monoblastic U937 cells. Expression of cytokine mRNAs such as TNF-alpha and IL-1 beta induced by LPS was inhibited by treatment with DY-9973 in U937 cells. Meanwhile, DY-9973 did not inhibit IL-1 beta-induced TNF-alpha production in U937 cells. TNF-alpha production induced by LPS or IL-1 beta was similarly inhibited by treatment with herbimycin, a tyrosine kinase inhibitor. Pretreatment with DY-9973 inhibited the elevation of serum TNF-alpha activity induced by the injection of LPS and reduced the lethal toxicity of LPS in BCG-primed mice. These results suggest that monosaccharidic lipid A analog such as DY-9973 can inhibit LPS-induced activation of macrophages and that it reduces lethal toxicity of LPS.

Cytokine-inducing components of periodontopathogenic bacteria

Pro-inflammatory cytokines such as interleukin (IL)-1, IL-6, IL-8 and tumour necrosis factor (TNF) are believed to be the major pathological mediators of inflammatory diseases ranging from arthritis to the periodontal diseases. The stimuli inducing proinflammatory cytokine induction in the former disease is unclear but in the periodontal diseases it is obvious that the stimulus is the accumulation of bacteria in the subgingival region. As these bacteria do not invade the lesional tissues in large numbers, it is believed that their soluble components or products interact with host tissues to induce cytokine gene transcription. The paradigm is that lipopolysaccharide is the key bacterial component inducing pro-inflammatory cytokine gene expression. However, over the past decade a growing number of reports on non-oral bacteria have established that many other bacterial components, as well as secretory products, have the capacity to induce cytokine synthesis. Some of these, such as the protein pneumolysin from Streptococcus pneumoniae, are incredibly potent (in this case inducing cytokine synthesis at femtomolar concentrations). This review surveys the range of bacterial components and products which have been shown to stimulate cytokine synthesis with particular emphasis on the hypothesis that these components play a role in the pathology of the periodontal diseases.

Hepatic sinusoidal endothelial cell in alcoholemia and endotoxemia

The experimental data reviewed in this study tend to indicate that the hepatic sinusoidal endothelial cell (SEC) is, chronologically, the first hepatic cell that undergoes pathologic changes in alcoholemia. Due to its strategic position in the liver sinusoid, SEC dysfunction and structural alterations have far-reaching repercussions for the whole liver. The authors gather experimental evidence suggesting that alcohol-induced SEC alterations are mostly due to Kupffer cell activation induced by alcohol rather than to a direct action of alcohol on SEC. Once activated, the Kupffer cell secretes a spectrum of mediators that affect both function and structure of SEC. Kupffer cell activation is regarded as a result of both direct and indirect actions of alcohol on the cell. The indirect action of alcohol is ascribed to alcohol-induced elevated plasma levels of Gram-negative bacterial lipopolysaccharide (LPS), a strong activator of Kupffer cell. However, a comparison of alcohol and LPS effects on SEC functions and structure reveals that these two agents may have, under many circumstances, different actions on the SEC, at least in laboratory animals. However, this issue continues to be a matter of debate. Also the review presents justification for the necessity to extend research on mechanisms underlying alcoholic liver disease to the effects of alcohol on the SEC. Finally, several future research directions are suggested in this review to better understand the mechanisms underlying alcohol-induced liver dysfunction.

Osteoclast activation in inflammatory periodontal diseases

OBJECTIVE

In this paper, we review the mechanisms thought to be involved in the activation of osteoclasts in periodontitis.

SUMMARY

Osteoclasts are regulated by both microbial and host factors. Some factors act directly on cells of the osteoclast lineage, whereas others act indirectly through other cell types in the bone environment. The proinflammatory cytokines (interleukins 1 and 6, tumor necrosis factors) have been implicated in the stimulation of osteoclastic resorption. The roles of the immunoregulatory cytoknes (interleukins 2 and 4, interferon gamma) are less clear, but decreased levels of these factors may contribute to periodontitis. A number of lipid mediators may be involved in stimulation of bone resorption. These include bacterial lipopolysaccharide and host-derived platelet-activating factor and prostaglandins. More recently, reactive oxygen intermediates and extracellular nucleotides, both present at sites of inflammation, have been investigated as possible modulators of osteoclast activity. The potential use of antiresorptive therapies in periodontitis is reviewed.

CONCLUSIONS

A wide range of host and bacterial factors contribute to the loss of alveolar bone in periodontitis. However, much remains to be understood about the complex mechanisms through which these factors regulate osteoclast activity. Further studies at the cellular and molecular level will lead to a better understanding of these processes and perhaps suggest new approaches for periodontal therapy.

Bacterial modulins: a novel class of virulence factors which cause host tissue pathology by inducing cytokine synthesis

Cytokines are a diverse group of proteins and glycoproteins which have potent and wide-ranging effects on eukaryotic cell function and are now recognized as important mediators of tissue pathology in infectious diseases. It is increasingly recognized that for many bacterial species, cytokine induction is a major virulence mechanism. Until recent years, the only bacterial component known to stimulate cytokine synthesis was lipopolysaccharide (LPS). It is only within the past decade that it has been clearly shown that many components associated with the bacterial cell wall, including proteins, glycoproteins, lipoproteins, carbohydrates, and lipids, have the capacity to stimulate mammalian cells to produce a diverse array of cytokines. It has been established that many of these cytokine-inducing molecules act by mechanisms distinct from that of LPS, and thus their activities are not due to LPS contamination. Bacteria produce a wide range of virulence factors which cause host tissue pathology, and these diverse factors have been grouped into four families: adhesins, aggressins, impedins, and invasins. We suggest that the array of bacterial cytokine-inducing molecules represents a new class of bacterial virulence factor, and, by analogy with the known virulence families, we suggest the term "modulin" to describe these molecules, because the action of cytokines is to modulate eukaryotic cell behavior. This review summarizes our current understanding of cytokine biology in relation to tissue homeostasis and disease and concisely reviews the current literature on the cytokine-inducing molecules produced by gram-negative and gram-positive bacteria, with an emphasis on the cellular mechanisms responsible for cytokine induction. We propose that modulins, by controlling the host immune and inflammatory responses, maintain the large commensal flora that all multicellular organisms support.

Microspheres based detoxification system: a new method in convective blood purification

A variety of protein-bound or hydrophobic substances, accumulating as a result of pathologic conditions such as exogenous or endogenous intoxications, are removed poorly by conventional detoxification methods because of low accessibility (hemodialysis), insufficient adsorption capabilities (hemosorption), low efficiency (peritoneal dialysis), or economic limitations (high-volume plasmapheresis). Combining advantages of existing methods with microspheric technology, a module-based system was designed. Major operating parameters of the latter can be modified to allow for adjustment to individual clinical situations. An extracorporeal blood circuit including a plasmafilter is combined with a secondary high-velocity plasma circuit driven by a centrifugal pump. Different microspheric adsorbers can be combined in one circuit or applied in sequence. Thus, a prolonged treatment can be tailored using specially designed selective adsorber materials. Comparing this system with existing methods (high-flux hemodialysis, molecular adsorbent recycling system), results from our in vitro studies and animal experiments demonstrate the superior efficiency of substance removal.

Syntheses of 1-O-carboxyalkyl GLA-60 analogues

As part of our ongoing study to survey potent LPS antagonists, the following six compounds were synthesized in an efficient manner: 3-carboxypropyl and carboxymethyl 2-deoxy-2-(2,2-difluorotetradecanamido)-4-O-phosphono-3-O-[(R)-3- (tetradecanoyloxy)tetradecanoyl]-alpha- and beta-D-glucopyranosides (11 and 23; 32 and 36), as well as the non-fluorinated equivalents, carboxymethyl 2-deoxy-4-O-phosphono-2-tetradecanamido-3-O-[(R)-3-(tetradecano yloxy)- tetradecanoyl]-alpha-D-glucopyranoside (44) and carboxymethyl 2-deoxy-2-[(R)-3-(hydroxy)tetradecanamido]-4-O-phosphono-3-O-[(R)- 3- (tetradecanoyloxy)tetradecanoyl]-alpha-D-glucopyranoside (48). Of these compounds, 32 was most pronounced in terms of LPS-antagonistic activity.

A novel Escherichia coli lipid A mutant that produces an antiinflammatory lipopolysaccharide

A unique screen was used to identify mutations in Escherichia coli lipid A biosynthesis that result in a decreased ability to stimulate E-selectin expression by human endothelial cells. A mutation was identified in the msbB gene of E. coli that resulted in lipopolysaccharide (LPS) that lacks the myristoyl fatty acid moiety of the lipid A. Unlike all previously reported lipid A mutants, the msbB mutant was not conditionally lethal for growth. Viable cells or purified LPS from an msbB mutant had a 1000-10,000-fold reduction in the ability to stimulate E-selectin production by human endothelial cells and TNF alpha production by adherent monocytes. The cloned msbB gene was able to functionally complement the msbB mutant, restoring both the LPS to its native composition and the ability of the strain to stimulate immune cells. Nonmyristoylated LPS acted as an antagonist for E-selectin expression when mixed with LPS obtained from the parental strain. These studies demonstrate a significant role for the myristate component of LPS in immune cell activation and antagonism. In addition, the msbB mutant allowed us to directly examine the crucial role that the lipid A structure plays when viable bacteria are presented to host defense cells.

Molecular mechanisms of endotoxin activity

Endotoxin (lipopolysaccharide, LPS), a constituent of the outer membrane of the cell wall of gram-negative bacteria, exerts a wide variety of biological effects in humans. This review focuses on the molecular mechanisms underlying these activities and discusses structure-function relationships of the endotoxin molecule, its interaction with humoral and cellular receptors involved in cell activation, and transmembrane and intracellular signal transduction pathways.